This invention relates to a rotary control spool for controlling a closed hydrostatic circuit. Currently there are two types of rotary control spools. A first that provides a linear response to a control input but results in such an aggressive response that it is required to utilize a small bleed orifice connecting the system ports in the hydrostatic pump to dampen the apparent response. The use of this small orifice carries with it a unique set of problems such as excess heat and poor efficiency. A second type of spool is one that utilizes metering of its ports. By metering, the spool allows for a smooth or “feathering” operation. Though this provides a softer control response and eliminates the need for the bleed orifice, there are certain applications wherein this metered control spool does not offer adequate response to the operator input. Therefore there is a problem in the art in that it is desired that an operator have a rotary control spool that allows for an aggressive response yet is still smooth enough so that a bleed orifice does not have to be utilized.
Therefore, it is a primary object of the present invention to provide a rotary control spool for an axial piston servo pump control that improves upon the state of the art.
Another object of the present invention is to provide a rotary control spool that meters its drain port to allow for a smooth operation.
Yet another object of the present invention is to provide a rotary control spool that utilizes a notch that tapers inwardly to a point that increases the spool porting area in order to provide an aggressive response.
Another object of the present invention is to use the combination of the metered drain port with the notch that tapers inwardly to a point that increases flow area in order to provide a rotary control spool that allows for an aggressive response and yet provides a smooth operation.
These and other objects, features, or advantages of the present invention will become apparent from the specification and claims.